Posted
by
samzenpus
on Thursday April 19, 2012 @06:42PM
from the space-anchor dept.

First time accepted submitter gstrickler writes "After years of work recovering and analyzing old mission data and vehicle schematics, a just published analysis(Pdf) provides strong evidence for anisotropic thermal radiation being the source of the slowing of the Pioneer 10 and 11 spacecraft. The theory isn't new, but the recovered data and new analysis provide solid evidence that at least 80% of the deceleration is accounted for by anisotropic thermal radiation. Members of The Planetary Society were instrumental in recovering the data and helping fund the analysis. The lesson is, in space, it matters what direction your heat radiating surfaces point."

Faster, slower - just depends on where the heat is being emitted - either towards where the craft is going (mainly the case here) or back towards where it came from.

In space, speed is a meaningless attribute without a point of reference. As well, space is non-euclidean in nature -- you can travel in a straight line and wind up in the same place you started. It's better to speak in terms of vectors and delta...

Heliocentrism is just as wrong as Earth Centrism. There is no "center" all things are relative. The concept of "speed" is flawed.

Consider the concept of two ships, heading in opposite directions each traveling at the "speed" of light (C), how fast are they going relative to each other? The flaw comes not from the "speed" but from the reference point at which one measures "speed"; you change the perspective you change the equation, and that changes everything.

Well actually, if they'd anticipated this and pointed the heat dissipating surfaces to the rear, Pioneer would be going faster.What the article did not state was how long it would take for these forces to cease forward momentum -- or if that is an issue.

What about pointing them sideways, backwards in relation to your orbital movement direction? The probes don't fly straight away from the Sun, that would waste enormous amounts of fuel due to actively fighting the gravity. Instead, they move in an increasingly wide orbit, by increasing orbital speed they make the orbit longer.

Anyway, imagine GP's idea with whatever vector of travel you've got, just pointing the heat radiation backwards so as not to impede your progress.

There are degrees, if you will, of backward pointing, from perpendicular and not affecting the travel vector, to nearly directly back and maximizing forward thrust, to directly back and catching maximal solar radiation.

Well actually, if they'd anticipated this and pointed the heat dissipating surfaces to the rear, Pioneer would be going faster.

I'm not sure they'd have done anything... the effect is so small, completely irrelevant for the main part of the missions, and they might have other reasons for orienting the craft a certain way -- maybe to maximize cooling. As a rule the side that emits the most photons would also be absorbing the most from the sun. I realize the situation could be more complicated than this; if it was simple the result would have been calculated a long time ago.

What I'm wondering is how many people will remove this from their "these handful of unexplained results in not fully understood circumstances mean all of physics are wrong (and my pet theory is right)" lists?

Could one compromise and put the radiators perpendicular to the direction of the sun (and travel?) eg, not on the front or back, but on the sides? Provided you did so equally, any force resulting in their radiation should cancel itself out.

That's what I was going to say at first but I wanted to lead into the cooling thing -- anticipating the follow-on that they craft could have been designed differently to both radiate heat and radio in the same direction. Somehow.

What I'm wondering is how many people will remove this from their "these handful of unexplained results in not fully understood circumstances mean all of physics are wrong (and my pet theory is right)" lists?

None. They'll just claim it's a worldwide conspiracy of physicists publishing only articles conforming to the official story to keep funding. And if that fails they'll ask for unfiltered instrument readings: if those aren't provided then the scientists are hiding something, and if they, the inevitable

Though on the other hand it's been nearly a decade since I've heard the solar neutrino problem brought up as an obvious reason why everything mainstream physics thinks is wrong and [kooky theory] is totally obvious if you aren't a member of the Scientific Clergy.

I think a lot of them will just move on using whatever other "anomalies" they please and ignore the times where they said "this means I'm right!" and they turn out to be wrong. Classic selection bias.

Not really as long as you realize that some things seem obvious once you know they're true... Or as long as you just mean "obvious possibility".

It's not like they didn't know that if there was a favored direction for the emission of radiation that this would affect the velocity of an object. The concept of a photon drive existed for decades before the Voyagers were launched. It's just that it was though that whatever net force there was would be essentially zero. Assume a uniform, spherical Voyager craft...

This has been a long-standing possible, and then probable, explanation for the anomaly. Seems to have taken quite a bit of effort to figure out what the actual value of the force would be with sufficient precision. I remember what seems like a long time ago an article posted to/. about someone calculating the effect of heat radiation using Phong shading, the 3D graphics technique, as an approximation and got pretty good agreement.

Going all the way to a complete finite element analysis, using multiple methods to come up with the coefficients for the model, and getting a result that leaves only a noise-level signal is pretty impressive. And not what I'd call obvious.

So despite maybe feeling like it, it's not exactly a case of research by the Maximegalon Institute of Slowly and Painfully Working Out the Surprisingly Obvious.

What the article did not state was how long it would take for these forces to cease forward momentum -- or if that is an issue.

I'm more worried about how long it will take before it plunges back to Earth. But on a more serious note, I think the energy source that is causing the heat will run out before either of those events happen, and if not, hopefully Earth will be in a different place in its orbit than it was when Pioneer was launched when it flies past on its way back.

I wouldn't worry about that seeing as its velocity is enough to escape our solar system [wikipedia.org] altogether. It's more likely to get closer to Aldebaran, a star currently 68 light years away, than our own Sun... given 2 million years or so that is.

Correct, and yet, this loss of speed has cost it about 250k mi in it's first 34 years. On a percentage basis, it's irrelevant, but over time it adds up. Here's an older article [space.com] on the anomaly

The discrepancy caused by the anomaly amounts to about 248,500 miles (400,000 kilometers), or roughly the distance between Earth and the Moon. That's how much farther the probes should have traveled in their 34 years, if our understanding of gravity is correct....

The drift showed that the Pioneers were being accelerated toward the Sun (or, rather, decelerated in their movement away from the Sun) by a tiny but inexplicable amount. The level of drift is equal to a gravitational effect 10 billion times weaker than the pull of Earth.

Sorry to self-correct - acceleration is a vector, it has both magnitude and direction. By summing all of the acceleration vectors, you get a resultant which determines the rate of change of your velocity.

Your post and its high moderation made me feel overeducated, so I wrote a poem in archaic style to reinforce the feeling.

Today I chanced to Look Down from my Ivory Tower;
the Vision horrified me.
I saw the Peasants Clamoring blindly
for the Simplest Certain Knowledge
of the Calculus and of Physicks.
I saw the Depth of Divide betwixt us thus:
One Man's Hidden Knowledge is Offal to th' Other.

P.S. To be fair, the stuff you mentioned is somewhere around the programming equivalent level of "objects can have properties".P.P.S. Also, note the pun on "offal"/"awful" in the last line. It's the only good line of the poem. It's true in at least 4 ways.P.P.P.S. Sorry for such a weird post. Maybe it'll amuse someone.

There's an acceleration vector for every force vector and a net acceleration and a net force vector. They're mathematically equivalent. You could also look at it as a sum of momentum delta vectors. How is the electromagnetic force conveyed? By a photon exchanging momentum. So is force something that only exists as an effect of adding up all the changes in momentum, or vice versa? Neither, both are correct viewpoints. Have a nice day.

The forces cannot be inferred by the acceleration, thus disproving your point.

You can't infer the forces from the net acceleration, you can't infer the accelerations from the net force, what is your point? Physically, the "force" keeping you from falling through your chair is being transmitted via discreet transfers of momentum and the 'force' field is just a consequence. But you can still talk about forces. You're not wrong about that, you're just wrong that it's wrong to talk about accelerations or changes in momentum adding to produce a net force. F = dp/dt. It's not a one-wa

It's rather easy to infer the acceleration from the resulting force (and mass). But why do you keep talking about "accelerations" (plural)? A ridgid body can only have one acceleration. (As the grandparent previously correctly stated.)

This is high school physics, more specifically Newton's laws of motion. It's not as if this is really that hard to understand:

Acceleration is defined as the rate of change of velocity, dv/dt, so, each of these "accelerations" will result in "velocities" (again plural), and using the definition for velocity, i.e., rate of change of position, or dp/dt, we get multiple positions. So, a direct consequence of your "accelerations" is "positions" (plural!), all for the same mass! I've never observed anything like that, nor have I ever heard of anybody observing it. If you have any evidence of this, I'd very much like to see it.

Heh, well, you certainly have a high-school physics understanding. Such as not realizing that you have observed this in every experiment you've ever conducted; or conversely that if your conception was correct that every 'acceleration' you've ever claimed to measure was wrong and you should have failed high school physics. After all, how often when calculating the force on an object did you add in the force of gravity from the sun, or the center of the galaxy, the Andromeda galaxy, etc. Never I'd wager.

While what you say about Galilean invariance is true, it has no implication on the current discussion. For each inertial frame you only have one acceleration per ridgid body.

Your words were:

If I have Ftot = F1 + F2, then I can say that atot = Ftot/m, or I can say that a1 = F1/m and a2 = F2/m and atot = a1 + a2.

a1 and a2 are accelerations the body experiences. Like forces, they add as vectors to get a net result. It's as valid as talking about the forces adding. If you think there's no component acceleration, then that's equivalent to saying that there's no component force, only a net force. Well, in a sense you could say that a rigid body can only experience one net force. But to then go "what do you mean forces, plural?" would be to miss the broader perspective.

Clearly you were talking about the "accelerations" in one inertial frame, not in multiple. So sorry, but you can't weasel yourself out of this discussion by refering to Galilean invariance.

Now, let's use the above on your example: Me sitting on a chair. According to you there is an acceleration from the pull of grav

its accelerating backwards... ie, it's effectively got its "engine" (ie the heat radiating surface) pointing in the direction its heading, and this is slowing it down. I guess its still got a lot of velocity, but this is being reduced by the lack of anything pushing it in the right direction.

Numerous investigators have been strengthening the case for thermal radiation as the cause for nearly a decade. The work of Bertolami, Francisco, et al in Portugal in 2008-2009 accounted for 67% of the acceleration, a then-new high point in this reckoning. This was a notable result, but they didn't "figure it out" or "solve" it, they strengthened the case that was by then widely believed to be correct. For an account of the whole story up through 2010 see: http://arxiv.org/pdf/1001.3686v2.pdf [arxiv.org].

The new study raises the level of confirmation to 80%, using data that they newly recovered, and further shows that the remaining 20% is not statistically significant. It is this study that deserves to be regarded as having "solved" the problem: accounting essentially for the full anomalous acceleration, and leaving no residual anomaly.

Yep. These guys are coming to the same conclusion. Too bad that the title in slashdot claims it to be "solved" - the new paper does not claim to have it solved - merely to have reached the same conclusion with (what appears to be) a higher confidence level.

Ah, that was the Phong shading one! Only in 2009? Seemed like longer ago...

At the time people were saying "Oh, why Phong shading? What's so perfect about that?" and, well, the answer is it isn't, it's an approximation. Not a bad one, either, but still. So's the finite element analysis these folk did. Just a much better one.

In the orginal article about it in the Planetary Report (from the Planetary Society) the answer was yes! The spacecraft with their little p$rno plaques meant for salacious alien entertainment will loop back to our solar system...
I don't know if that conclusion is still operative.

In a sense yes. Radiation and all other forms of energy have relativistic mass, as in the m in E=mc^2, as in things that have more energy (moving objects, high-energy states of atoms and molecules, systems in general) have more mass as it applies to inertia and gravity.

Heat radiation as in (mostly infrared) photons don't have rest mass. That's the m0 in E = root(pc^2 + m0^2*c^4). So they don't have mass in the sense of matter as you usually think of it. But it turns out the way you usually think of mass is not equivalent to matter. Even though the usual way you think about it is that they are.

I thought that E=mc^2 meant that E could me converted to M not that all it was both energy and mass at the same time.And that massless photons when shot in one direction actually push back in the other.

I thought that E=mc^2 meant that E could me converted to M not that all it was both energy and mass at the same time.

So did I! But it's not a conversion, it's an equivalence! Energy and mass -- relativistic mass, the quantity that informs our notions of gravity, weight, and inertia -- are really, always, the same thing just in different units. If there's more energy in a system, then it weighs more on a scale. Water weighs less than two hydrogen and one oxygen because it's at a lower energy state. This of course includes the energy that is in the form of rest mass.

Rest mass is a form of energy. It can be converted into other forms of energy at a rate equal to m0*c^2. Energy and relativistic mass are always related by the equation E=mc^2.

Air has a density of 1.204kg/m^3 at 20C, so a baloon with 3000m^3 of air has 3612kg of air. When we heat that air to 120C the density drops to 0.898kg/m^3 so 2694kg.

Now lets pretend the mass increase from heating magically applies to all the original air - 3612kg of it. Our temperature change is 100C == 100K. Heat capacity of air ranges from 1.005 to 1.013 over our temperature range. Since we're going for the overestimate lets say it's 1.013.

That's exactly the point of this new article, it confirms the theory by accounting reducing the variance to below the "noise" level. Scientifically and statistically speaking, it's a solid confirmation.

It is very nice to see this analysis come to a clear conclusion. There are many reasons for physicists and those who feel constrained by the laws of physics to wish for violations of known laws that have significant effects in our corner of the galaxy. But time after time mundane explanations based on known laws turn out to be right. At some point more people are going to catch that we are not going to continuously overturn accepted science. Eventually the philosophers and sociologists of science might

If I understand ion thrusters correctly (that's a big if), a big tank of neutral atoms are bombarded by electrons to knock other electrons out of orbit around those atoms, creating positive particles, which are electrostatically accelerated out a big metal screen thing and the motion of them going the opposite way makes your spaceship go the correct way.
I believe thermal radiation in this article's context means heat being turned into infrared light, that means photons going the opposite direction can have a noticeable impact on an existing spaceship in a real world text over a relatively short distance in space. I would think a gigantic atom nucleus has thousands of times more mass than a photon so ion thrusters would be pretty effective over time. Now of course the opposite "kick back" reaction is proportionate to the amount of energy you're putting into the ions and their speed is ohhhhh just a hair slower than a photon (lol) but at least we can say the theory should work in real space based on this experience.

A spacecraft dedicated to disproving this anomally should be slingshotted out of the solar system to test this once and for all and address the reamining 20%. It could be a cheap spin-stabilized craft with a pinger and a transmitter and carefully studied thermal characteristics.

They showed that the residual 20% is not statistically significant. This is a showing that there is no additional anomaly to be accounted for. This is what is called "solving a problem" in real science.

Nah. Crookes radiometer is not due to thermal radiation pressure in a vacuum. It is a ballistic effect of air molecules in a very thin atmosphere bouncing off a hot surface with more velocity than they had when the collided with.

No rest mass, but they do have relativistic mass, m_r = h*f/c^2, where h is Planck's constant, f is photon's frequency, and c is speed of light. And they are affected by gravity, a photon emitted from a flashlight held horizontal will fall on Earth a bit. That's why gravitational lensing works.